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Good news on COVID-19: Levels of coronavirus in Eastern Mass. waste water continue decline

The Deer Island treatment plant in Boston Harbor.David L. Ryan/Globe Staff

In another encouraging sign for those hoping for a respite from the Omicron surge, the amount of coronavirus detected in Eastern Massachusetts waste water has continued to fall in recent days, according to data released Tuesday by the Massachusetts Water Resources Authority.

The amount of virus flowing in from communities in the MWRA’s southern region is now less than one-tenth of what it was when the surge peaked early this year, while the amount flowing in from the northern region is less than one-eighth of what it was at its peak.

The amounts are similar to what the state saw in early December, just before the numbers began racing to stratospheric heights.


Officials from Cambridge-based Biobot Analytics, which conducts the testing, say they have found the amount of virus detected is correlated with newly diagnosed coronavirus cases several days later. So the declines in the amount of virus suggest there may be further declines in cases ahead. Official case numbers have also been steeply declining in recent weeks.

Waste water from 43 communities, including Boston, converges on the MWRA’s Deer Island treatment plant. There, the sewage is tested to determine the number of SARS-CoV-2 RNA copies per milliliter of waste water.

SARS-CoV-2 RNA is shed in fecal matter of infected people. Experts say the testing can be a complement to clinical testing, providing insight into the true number of how many people are infected. Clinical testing has its limitations because it depends on people knowing they’re sick, deciding not to test at home using rapid, antigen tests, and being able to schedule a PCR test.

For the southern MWRA region, the seven-day average was 1,118 RNA copies/mL as of Monday. That’s down from a high of 11,446 RNA copies/mL on Jan. 3.

In the northern region, the seven-day average was 1,016 RNA copies/mL as of Monday, down from 8,644 as of Jan. 5.


Martin Finucane can be reached at